The present invention relates to a method for cooling electronic components used within information instruments, imaging instruments, mobile telecommunication instruments, and other electronic instruments. More particularly, the present invention relates to a method for cooling electronic components by conducting the heat to a cooling member, such as a radiator and a thermally conductive metal plate, and a thermally conductive sheet for use with such a method.
As the performance of electronic components, such as CPUs, integrated in electronic instruments improves, the amounts of electric power consumption and heat generation have increased significantly. Consequently, cooling these electronic components has become an urgent problem that must be addressed in order to maintain the performances of the electronic components. For this reason, a demand exists for thermally conductive sheets having a high heat conductivity that are placed between an electronic component and a cooling member to conduct heat generated by the electronic component to the cooling member.
To meet such a demand, Japanese Laid-Open Patent Publication No. 2000-001616 discloses a method for densely filling a thermally conductive sheet with thermally conductive filler. Also, Japanese Laid-Open Patent Publication No. 2000-345040 describes a method in which a stick-shaped thermally conductive filler is oriented in a particular direction to increase the heat-conductivity in that direction to achieve an even high heat-conductivity.
In addition to high thermal conductivity, a thermally conductive sheet is required to have a high electrical resistance to serve as a good electrical insulator. For instance, when several electronic components are mounted adjacent to one another, a single thermally conductive sheet sufficiently large to cover all of the components is often used rather than using separate thermally conductive sheets, each having the substantially same size as the component, one for each component. When used in this fashion, the thermally conductive sheet comes into contact not only with the intended electronic components but also with other electrically conductive components, such as connection terminals and electronic circuits. For this reason, the thermally conductive sheets must have a high electrical resistance. Specifically, such a thermally conductive sheet must have an electrical resistance of 1.0×1010 Ω·cm or higher. To this end, conventional thermally conductive sheets included thermally conductive fillers having a high electrical resistance, such as alumina and magnesia.
However, recently developed high-performance electronic components generate significant amounts of heat. The conventional thermally conductive sheets that contain thermally conductive fillers having a high electrical resistance, such as alumina and magnesia, fail to provide a sufficiently high heat conductivity, in particular a heat conductivity of 6 W/m·K or more, to effectively conduct the heat generated by the high-performance electronic components to a cooling member.
A different type of conventional thermally conductive sheet contains thermally conductive filler of graphitized carbon powder and/or metal powder, each of which is a highly thermally conductive material. The thermally conductive sheet thus achieves a high heat conductivity of 6 W/m·K or higher. This type of thermally conductive sheet, however, has a low electrical resistance and may allow an undesirable electrical conduction near terminals and electronic circuits of the electronic components. As a result, such a thermally conductive sheet has a limited range of applications.
The high performance electronic components are densely integrated in newly developed electronic instruments and, therefore, a novel approach is demanded for effectively cooling these electronic components, such as a thermally conductive sheet that has a high heat conductivity of 6 W/m·K or higher as well as a high electric resistance of 1.0×1010 Ω·cm or higher.